Ensure messageCache is updated when properties are unset

Co-authored-by: trevor-signal <131492920+trevor-signal@users.noreply.github.com>

ts/jobs/helpers/sendReaction.ts

@@ -382,7 +382,7 @@ const setReactions = (
   if (reactions.length) {
     message.set('reactions', reactions);
   } else {
-    message.unset('reactions');
+    message.set('reactions', undefined);
   }
 };
 

ts/models/messages.ts

@@ -491,7 +491,7 @@ export class MessageModel extends window.Backbone.Model<MessageAttributesType> {
       }
 
       if (this.get('storyReplyContext')) {
-        this.unset('storyReplyContext');
+        this.set('storyReplyContext', undefined);
       }
       await this.hydrateStoryContext(message.attributes, { shouldSave: true });
       return;

ts/util/cleanup.ts

@@ -89,7 +89,7 @@ async function cleanupStoryReplies(
           reply,
           'cleanupStoryReplies/1:1'
         );
-        model.unset('storyReplyContext');
+        model.set('storyReplyContext', undefined);
         await model.hydrateStoryContext(story, { shouldSave: true });
       })
     );